The present invention generally concerns an improved coupling arrangement, and in particular concerns a vibration-proof splined coupling arrangement incorporating a clamping collar.
A most common need in drive applications is an effective coupling arrangement between the drive or power source (such as the output shaft of an electric motor), and the load to be driven (such as a gear reducer unit, conveyor belt, sprocket, or the like). In many instances, it is highly desirable, if not altogether an absolute requirement, that the load to be driven be removably engaged (i.e., separable) from the drive power unit. In other words, for maintenance, redesign, or other purposes, it is necessary or desirable to be able to de-couple the motor or other drive source from its load. Once de-coupled, it is also often desirable to effect whatever repairs, redesign, or reconfiguration desired in a minimum amount of time, to prevent extraordinary loss of output or production from the driven load, which may be part of a commercial process or the like.
Numerous different coupling arrangements are well known to those of ordinary skill in the art. For example, one approach is to make use of tapered bores mated with tapered bushings or the like, which results in an interference fit. Typically, in such arrangements one member may be extracted from the other through the use of jacking screws. Though widely and successfully practiced for numerous applications, existing field equipment and parts in some instances are simply not designed for use of tapered/interference-fit technology without total replacement or reworking of such existing parts.
Another approach totally separate from the interference-fit technologies involves use of matable splined shaft and splined bore members. In such cases, since an interference fit is not intended, several thousandths of an inch (0.001") clearance or the like is preferably provided, to permit ready alternate introduction and removal of the splined members, one to another.
Such splined technology, like the tapered/interference-fit technology, is generally widely used for various applications, and has experienced considerable success. On the other hand, the present invention recognizes and addresses a particular instance in which highly undesirable and destructive fretting corrosion occurs between the splined members, even to the point of resulting in a coupling failure, a worst case scenario.
Frequently, in particular coupling arrangements, the male splined member will be formed as a shaft, which in turn is integrally operatively incorporated into a commercial process. Obviously, certain commercial processes are more cost sensitive to downtime than others; but, in any event, it is highly desirable to minimize downtime. If there is a coupling failure due to fretting corrosion which can be avoided by an improved design, then perhaps an expensive input shaft will not need frequent replacing. On the other hand, if a drive motor or other component fails, necessitating separation of the drive motor from the load, the presence of fretting corrosion can render difficult, if not impossible, such separation. Such separation problems can result in even greater downtime than if the entire shaft were being replaced, such as in the first instance mentioned above.
Due to the relatively minute amount of clearance typically between splined members, the amount of play between such coupling members is likewise very minute. Thus, in an overwhelming number of applications, such splined coupling technology performs in a totally adequate manner, during both driven, coupling operations, and de-coupling operations. However, the present invention recognizes and addresses that certain types of loading conditions can nonetheless result in fretting corrosion to splined couplings. In some instances, the entire spline supported on the shaft can be eaten away by the iron oxide or red rusty powder which forms from such fretting corrosion.
The foregoing corrosion problems have been noted particularly in applications involving repetitive cycling of a system under one or more of heavy reversing conditions, frequent start/stop conditions, or other rapidly-alternating accelerating/decelerating loading conditions. In such instances, which typically comprise a very small percentage of most commercial uses, the present invention recognizes that the very small amount of play between conventional male and female splined coupling members ultimately results in the above-mentioned fretting corrosion.
Various solutions to eliminating such small amounts of play and backlash have been attempted. In one such instance, a set screw radially situated through the circumference of the female splined member is brought into contact with the male splined member. Not only does such an arrangement result in pitting and other damage to the splining of the male member, it nonetheless ultimately shakes loose under the above-mentioned heavy-duty, repetitive-cycling loading conditions.
In one variation to such set screw arrangement, the Lovejoy Coupling Company of Downers Grove, Ill. 60515, provides a splined shaft clamping hub known as the "Centaloc". Such technique involves use of a slot situated slightly above and parallel to the spline bore. One or two set screws are fitted perpendicularly into such slot. During torquing of the set screws, the spline shaft is not touched by the set screws, but instead is supposedly "wrapped" with a clamping force, which can be subsequently removed by loosening the set screw or screws. One particular problem with such design is that is has been found that providing adequate clamping force for clamping the spline shaft can result in literal breakage of the wrench used to torque the set screw(s). Even if the wrench does not break, it is difficult to achieve the necessary clamping force, or to know when such adequate force is effected.
For some users, the only available in-field expedient solution to the above-discussed problems has been to use "Loctite" or similar metallic glue products to bind the two splined members together. While such "brute force" technique obviously eliminates fretting corrosion by eliminating all play between the splined coupling members, it also just as obviously eliminates any possibility of subsequently separating such coupling members without damage thereto, and hence is clearly not a general, long-term practical solution to the above-mentioned problems.
As mentioned above, tapered/interference-fit technology may be one effective solution to the noted technical problems, but can be cost prohibitive to implement (i.e., retrofit) once a splined technology system is in place.